The present invention relates to the isomerization of paraffin containing hydrocarbon feedstock, and, in particular, to conversion by isomerization of n-paraffins, while maintaining a resistance to poisoning by nitrogen containing compounds.
Zeolite materials have been demonstrated to have catalytic properties for various types of hydrocarbon conversions. Certain zeolitic materials contain ordered, porous crystalline aluminosilicates having definitive crystalline structure, such as can be determined by X-ray diffraction, within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. The dimensions of these pores are such as to except for adsorption molecules of certain dimensions while rejecting those of larger dimensions. Furthermore, these materials may contain sites of reactivity to which the molecules can adhere or otherwise attach and be converted by, for example cracking, isomerizing, etc.
For example, in U.S. Pat. No. 4,257,872 to LaPierre, et al. there is disclosed a process for upgrading coke or gas oil by a low pressure catalytic hydrocracking of refractory hydrocarbon charge stocks. The Lapierre process contemplates initial hydrotreating of the refractory feed to convert sulfur, nitrogen and oxygen derivatives of hydrocarbon to hydrogen sulfide, ammonia and water while depositing metal contaminant from the hydrodecomposition of any organo-metal compounds. LaPierre, et al. indicate that the zeolites used therein have the ability to induce profound transformation of aliphatic hydrocarbons to aromatic hydrocarbons in commercially desirable yields and are generally highly effective in conversion reactors involving aromatic hydrocarbons. The process of LaPierre, et al. also contemplates the use of high pressure for purposes of hydrocracking the refractory hydrocarbon charge stocks, such as in the range of 100 to 3,000 psig. In fact, all of the pressures used in the examples shown therein include a pressure of at least a 1,000 psig.
In U.S. Pat. No. 4,247,388 to Banta, et al. a method is disclosed for improving catalytic hydrodewaxing of petroleum synthetic hydrocarbon feedstocks using acidic crystalline aluminosilicate zeolites such as those of the ZSM-5 type which involves treatment of the zeolites in order to adjust their initially high alpha activity to within a range of 55 to 150 alpha prior to use as catalysts in a hydrodewaxing operation.
In U.S. Pat. No. 4,229,282 to Peters, et al. an improved process for catalytically dewaxing a hydrocarbon oil is disclosed in which the waxy oil is contacted with a dense zeolitic dewaxing catalyst in the presence of hydrogen and in combination with a nickel-tungsten hydrogenation component. The dewaxed oil has good stability and low bromine number compared with prior-art processed oils. The process may be used to dewax crude oils, fuel oil fractions and lubricating oils.
U.S. Pat. No. 4,284,529 to Shihabi discloses a process for conversion of relatively heavy hydrocarbon streams to produce lower molecular weight materials in order to convert, for example, waxy crude petroleum in the field to products suitable for transmission by pipeline. The objective of "cracking" in the Shihabi '529 disclosure is to reduce the molecular weight number, and does not address the issue of isomerization in order to convert the paraffinic content of a hydrocarbon feedstock.
Thus, in the search to perfect an efficient process and catalyst, artisans in the area of hydrocarbon processing have begun to reject high pressure hydrodewaxing processes of the prior-art in order to achieve high distillate yield through hydroisomerization, and are engaged in searching for a truly low pressure isomerization procedure and poison resistant catalyst which will yield optimum distillate range hydrocarbon feedstock with an acceptably low pour point. Accordingly, the present invention has been discovered to provide a significant advancement in the search for such efficient procedure and catalyst.